Silica deposition in aqueous systems, for example cooling towers and hypersaline geothermal brines, has been a continual problem. They have, historically, been cleaned by blow-down. If deposition occurs, mechanical removal has been the method used. Obviously, this causes loss of time and increased energy and labor costs.
pH affects the ionization of silanol groups and, therefore, affects the polymerization rate. Silica first forms, then three dimensional networks and, eventually, colloidal particles grow through condensation. At pH 7, nuclei formation and particle growth is very rapid. The pH of cooling water is generally 6.0 to 8.5 and the water temperature is generally about 30.degree. to 70.degree. C. The pH of geothermal brines is generally 4.0 to 6.0 and the brine temperature is generally about 100.degree. to 210.degree. C.
It is known to use cationic polymers or cationic surfactants as silica scale inhibitors in hypersaline geothermal brines (Harrar, J. E. et al, "Final Report on Tests of Proprietary Chemical Additives as Anti-scalants for Hypersaline Geothermal Brine", January 1980, Lawrence Livermore Laboratory; Harrar, J. E. et al, "On-Line Tests of Organic Additives for the Inhibition of the Precipitation of Silica from Hypersaline Geothermal Brine IV. Final tests of Candidate Additives", February 1980, Lawrence Livermore Laboratories; and Harrar, J. E. et al, "Studies of Scale Formation and Scale Inhibitors at the Salton Sea Geothermal Field", Corrosion/80, Paper No. 225, International Corrosion Forum Devoted Exclusively to the Protection and Performance of Materials, Mar. 3-7, 1980, Chicago, Ill.).